Recovery Of Iron And Aluminum From Bayer Red Mud

The recovery and reuse of solid waste is a research highlights in the field of environment.Red mud is a solid waste which is produced in the alumina production.1.0-1.8 tons of red mud are produced along with every 1 tons of alumina production.The production of a large number of high alkaline red mud poses a great threat to the environment.Meanwhile,red mud contains a variety of valuable metals,especially iron and aluminum,which can be used as secondary resources for sustainable development and utilization.However,due to the similar properties,the existence of iron and aluminum in red mud leads to some difficulties for the recovery of other metals.Therefore,it is of great significance to give priority to the recovery of iron and aluminum in red mud.In this study,based on the high content of iron and Al in Bayer red mud form Guangxi Pingguo Aluminum Co.,Ltd.,in view of its high iron and aluminum content characteristics,a new two-stage acid leaching technology was proposed.Firstly,the red mud was leached with low concentration hydrochloric acid in one stage to enrich iron and aluminum.Then,the red mud was leached with oxalic acid in two stages to extract iron and aluminum.Based on the single factor experiment,the response surface design and optimization were carried out to determine the optimal conditions of iron and aluminum leaching from red mud with oxalic acid.Finally,iron and aluminum and oxalic acid were separated and recovered from the leaching solution.The main research results are as follows:(1)The results of the first-stage leaching of red mud with hydrochloric acid showed that:the concentration of hydrochloric acid is 1 mol/L,the L/S ratio is 6:1m L/g,reaction time of 60 min,reaction temperature of 65?,the leaching rates of Na,K,Ca,Fe and Al are 84.56%,65.53%,86.99%,0.11%and 11.09%respectively.At the same time,thermodynamic calculation result indicates that it is feasible to use low concentration hydrochloric acid for one-stage leaching reaction of red mud,and nepheline,calcite,pyrophyllite and sodalite in red mud are relatively easy to be leached,while hematite and diaspore are difficult to react with hydrochloric acid under this condition.(2)The optimal leaching conditions of Fe and Al from red mud by oxalic acid are as follows:the amount of oxalic acid is 4.22 g,the reaction temperature is 95?,the reaction time is 150 min,and the liquid-solid ratio is 14:1 ml/g.Under these conditions,the leaching rates of Fe and Al are 87.76%and 80.45%respectively.According to the leaching kinetics analysis,the chemical reaction diffusion control kinetic rate equation (?) is the reaction rate model of oxalic acid leaching Fe from red mud,and the internal diffusion control kinetic rate equation (?) is the reaction rate model of leaching Al.The above two kinetic rate equations well describe the leaching behavior of Fe and Al.(3)The separation and recovery of Fe,Al and C₂O₄^2-in the oxalic acid leaching solution were determined:the oxalic acid leaching solution was illuminated by sunlight to produce FeC₂O₄ precipitation,and more than 85% Fe could be recovered after 420 min of illumination.Aluminum hydroxide could be recovered by adding ammonia to the leaching solution after iron removal and adjusting the p H value to 10-11,while oxalic acid was recovered in the form of ammonium oxalate.After preliminary economic analysis,the proposed new two-stage acid leaching technology has a certain market competitiveness,which can alleviate the current environmental pressure brought by red mud,but also can bring certain economic benefits.